Androstenedione production rates; transfer rates to estrone and estrone productaon rates are being measured in post-menopausal women with carcinoma of the breast, in an attempt to detect abnormalities in androgen-estrogen production. To date 25 women with Ca of breast have been so studied. Androstenedione production rates are unchanged from normal women and women with non-breast ca. Transfer rate (rho) of androstenedione to estrone are similarly not different in women with breast cancer. Estrone metabolic clearance rates, however, in women with ca. of the breast show considerably wider scatter (on the high side) with many patients exhibiting increased metabolic clearance rates. Mean MCRE was 2580 plus or minus 233 L/day vs. 1930 plus or minus 160 in women with non-breast Ca and 1720 plus or minus 140 in lNon-Ca control patients. The significance of the increased MCR of estrone in women with Ca. of the breast is being investigated.